The US, Australia and Japan have promised to continue "freedom of navigation" operations in the South China Sea and called on Beijing to endorse a legally binding code of conduct over the disputed region.

In a joint statement following a meeting Monday of US Secretary of State Rex Tillerson and his Australian and Japanese counterparts, the three officials "expressed serious concerns over maritime disputes in the South China Sea."

The three foreign ministers also said they would "continue to fly, sail, and operate wherever international law allows."

They urged all claimants in the region to "refrain from land reclamation, construction of outposts, militarization of disputed features, and undertaking unilateral actions that cause permanent physical change to the marine environment in areas pending delimitation."